System and Method for Optimized Encoding and Transmission of a Plurality of Substantially Similar Video Fragments

ABSTRACT

A system and method for stitching separately encoded MPEG video fragments, each representing a different rectangular area of the screen together into one single full-screen MPEG encoded video fragment.

FIELD OF THE INVENTION

This invention is directed towards digital compressed video, and moreparticularly towards a method for merging separately encoded MPEG videosegments into a single full-screen encoded MPEG video segment.

BACKGROUND

Current electronic distribution of television messages, such ascommercials, from an originator or distributor to one or more televisionbroadcast stations and/or cable television master control centers, doesnot easily allow for regional customization of such messages. The reasonfor this is that each different variant of a message has to betransmitted completely by itself, and independent from the othervariants, from sender to receiver. Each extra variant will thus requireproportionally extra bandwidth usage over the transmission channel.Sending fifty different variants will require fifty times as muchbandwidth as sending one single variant. This added bandwidthconsumption would be prohibitively costly and/or time consuming.

Regional customization of television messages would be desirable, forexample, in the distribution of infomercials. An infomercial is atelevision commercial with the specific purpose of getting the viewer topickup the phone and order the advertised product immediately.Typically, there are two types of infomercials: Long form messages (paidprogramming), having a length of (approx.) 30 minutes, and short formmessages (direct response ads, aired in the space of normalcommercials), having a length of 30-120 sec.

A typical infomercial (just like any other television commercial) isbroadcast in many different geographic regions from many different(easily 50 or more) broadcast stations. To measure the effectiveness ofthe commercial in the different regions it would be advantageous to havea different call-in phone number in use for the commercial in eachregion. Typically, such phone numbers to be called by the viewer areoverlaid over a small portion, typically the bottom, of the video forthe entire duration (or large portions) of the commercial.

Regional customization of television messages would also beadvantageous, for instance, in the case of a commercial for a brand orchain that has many stores throughout the country. Commercials for thebrand could be regionalized by showing the address of the nearest storefor that brand, by showing different promotions for different productsfor each region, by showing different prices for the same product indifferent regions, etc. Such region-specific customizations could beadded to small portions of the video of the commercial, for example as(but not limited to) a text overlay.

The above examples have in common that a small portion of the video isvarying between the different versions of the message, while largerportions of the video are common between many versions. Therefore itwould be advantageous if there was a method to independently encode anddistribute different portions of the screen, to exploit the differentamounts of variation for different portions of the screen, and thusachieve a saving in required transmission bandwidth. An additionaladvantage would be reduced encoding and decoding time since the amountof video to be encoded and decoded would be less.

However, television commercials are currently mainly distributed inMPEG-2 format. Unfortunately, the MPEG-2 video compression standard aswell as existing MPEG-2 encoding and decoding equipment do not allow forindependent encoding, decoding, and/or assembly into full screen video,of different portions of the video screen.

SUMMARY

“Video stitching” is a solution to the problem of how to efficientlyencode, bundle, and assemble many different variants of a single pieceof digital video, where certain (preferably small) rectangular parts ofthe screen can be identified as containing a lot of variations, and theremaining, preferably large, rectangular portion(s) of the screen areinvariant (or have very little variation) across all versions of thevideo.

In a situation where only parts of the video, for instance the bottom,are different over all variants, it is advantageous to encode only onecopy of the (common) top of the screen and multiple different copies ofthe bottom of the screen than to encode each full-screen variant. At thereceiving end, a video stitching system would be used to reconstruct anydesired variant. Savings will be made both in speed of encoding,decoding, and size of the complete package with all variants.

An illustrative embodiment of the present invention includes a method ofencoding partial-frame video segments, the method including dividing thefull-video frame area into rectangular regions, wherein the rectangularregions have a length and width that are each a multiple of 16 pixels.Then upon obtaining video segments for at least one of the rectangularregions, the method includes determining a target VBV buffer size forthe video segments for a selected rectangular region, and then encodingthe video segments for the selected rectangular region using thedetermined target VBV buffer size. Preferably, a common GOP pattern isused for encoding all video segments for all of the rectangular regions.

The step of determining a target VBV buffer size includes selecting atarget VBV buffer size that is substantially proportional to a fullframe VBV buffer size based on relative size of the rectangular regionas compared to a full frame size. Alternatively a target VBV buffer sizeis selected that is smaller than a value that is substantiallyproportional to a full frame VBV buffer size based on relative size ofthe rectangular region as compared to a full frame size. The method alsoincludes determining a VBV bit rate for encoding the video segments forthe selected rectangular region, wherein the VBV bit rate is selectedthat is substantially proportional to a full frame VBV bit rate based onrelative size of the rectangular region as compared to a full framesize. Alternatively, a VBV bit rate is selected that is smaller than avalue that is substantially proportional to a full frame VBV bit ratebased on relative size of the rectangular region as compared to a fullframe size.

The illustrative embodiment also includes determining f-code arrayvalues for the video segments, after encoding the video segments,modifying the f-code array values and motion vectors for the encodedvideo according to the determined f-code array values. The f-code arrayvalues are determined by using the maximum values for the f-code arrayvalues from the plurality of video segments.

The illustrative embodiment also includes assembling a row of encodedvideo segment macroblocks into a slice, wherein header information foreach macroblock in the slice is modified for a proper format for acomplete slice.

The method also includes obtaining a plurality of different videosegments for the rectangular region, wherein the different videosegments are then merged with other video segments for other rectangularregions to create multiple different full-video frame video segments.

The present invention also includes an encoding system for encodingpartial-frame video segments to allow different partial-frame videosegments to be merged into a full-video frame.

The savings in overall package size as provided by the present inventionis important, for instance, in situations of satellite(multicast/broadcast) distribution of the entire package from theoriginator to the local broadcast stations. Each local station has toextract the desired variant from the package. This is shown in FIG. 2.Large savings in the size of the package to be distributed will make itcommercially feasible to have many different variants of theinfomercial.

Even in the case of (unicast) distribution of the entire package from asingle originator to a single intermediate distribution point (such as acable television local advertising master control center) the savings inbandwidth between originator and distribution point will allow for majorcost and time savings.

It is important to note that Video Stitching as described in the presentinvention is very different from other object-based compressed videotechnologies (such as MPEG-4) since the order of decoding and composing(stitching) the individual segments is reversed. In MPEG-4, the videodecoder first decodes the various encoded video segments, and thencomposes the resulting uncompressed segments (typically on-the-fly) intofull screen video. In the proposed video stitching method, thecompressed segments are first stitched together into a full-screencompressed segment which is subsequently decoded.

Another difference between the present invention and other object-basedvideo compression methods such as MPEG-4 is that Video Stitching asdescribed integrates naturally with existing MPEG-2 decoding equipmentdeployed in, for example, cable television headends and broadcasttelevision stations. To support video stitching in such environmentswould mean that the individually encoded MPEG video segments arestitched together just after reception at the point of decoding.Decoding itself will not change since the Video Stitcher will producethe same type of (MPEG-2) streams that are currently handled by suchsystems. As a comparison, using MPEG-4 would mean that a transcoder fromMPEG-4 to MPEG-2 is needed at the point of reception to be able to reusethe existing MPEG-2 decoders, which is disadvantageous. Another optionwould be replacing the existing MPEG-2 decoders with MPEG-4 decoderswhich is disadvantageous from a cost perspective.

Note that the present invention will work with videos of any resolution,and is not restricted to just NTSC or PAL. Any resolution that is legalunder MPEG is supported.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the present inventionwill be more fully understood from the following detailed description ofillustrative embodiments, taken in conjunction with the accompanyingdrawings in which:

FIG. 1 illustrates a video segment split-up in a top and bottom region;

FIG. 2 illustrates a satellite broadcast of a package consisting of asingle top video file and multiple bottom video files;

FIG. 3 illustrates a video segment split-up into five differentrectangular regions;

FIG. 4 illustrates a video segment split-up into seven differentrectangular regions;

FIG. 5 illustrates part of preparing stitchable video segments andstitching them together into valid MPEG, according to an illustrativeembodiment; and

FIG. 6 illustrates another part of preparing stitchable video segmentsand stitching them together into valid MPEG according to an illustrativeembodiment.

DETAILED DESCRIPTION

A method of creating personalized messages that can be used forregionally, or even personalized, targeting based on variations in thecommercial is described in co-pending U.S. patent application Ser. No.09/545,015 filed on Apr. 7, 2000 and incorporated herein by reference.The present invention is directed towards variations between video andcommercials based on differences that are confined to certain portionsof the screen.

The present invention finds utility in various data transmissionapplications including, but not limited to, encoding, transmission,reception and decoding of digital compressed video, regardless of themeans of transmission.

An application of an illustrative embodiment is shown in FIG. 1. A pieceof video 20 is to be created of which fifty variations must be made,each with a different 1-800-number, promotion code, or any other pieceof information in the bottom ⅓^(rd) of the screen. The final videos haveto be encoded in MPEG-2, have a total resolution of 720×480 (NTSC) and abitrate of 4,500,000 bps. The top video will have a resolution of720×320 and an encoding bitrate of 3,000,000 bps. The bottom video willhave a resolution of 720×160 and an encoding bitrate of 1,500,000 bps,leading to the desired merged resolution and bitrate. Typical MPEG VBVbuffer size values will be 140 Kbyte for the top and 70 Kbyte for thebottom (leading to a an overall VBV buffer size after merging below themaximum of 224 Kbyte).

Now, assuming a thirty minute message, fifty completely encoded variantswould require a total storage capacity (and transmission bandwidth) of(30×60×4.5×50)/(8×1024)=50 Gbyte. Separate encoding of the single topsection and the 50 different bottom sections will only require(30×60×(3+1.5×50))/(8×1024)=17 Gbyte, which represents a reduction insize of a factor 3 (34% of the full size).

In situations where the bottom section is smaller and/or the amount ofdifferent variants is larger the savings will increase even moredramatically. For example, a bottom section of ⅕^(th) of the screen sizeand a total of 100 variants will lead to a size of 100 Gbyte forencoding of each full variants, and30×60×4.5×(4/5+1/5×1.00)/(8×1024)=20.5 Gbyte for separate encoding ofthe top part and the bottom parts. This reflects a reduction by a factorof 5 (20% of the full size).

FIGS. 5 and 6 describe the various steps in preparing stitchable videosegments, and stitching such video segments together into fill-screensegments. Throughout the following text references will be made to thesteps shown in these pictures as further illustration of the presentinvention.

A first aspect of the present invention is how to encode the video tomake it suitable for stitching at a later point in time. One possibilityis to encode all variant commercials in their full-screen entirety, andthen post-process them into the separate parts. This has proven to benot practical because MPEG motion vectors allow video at any given pointon the screen to “migrate” to other parts of the screen over time (theduration of a GOP (Group of Pictures) is typically half a second), andit cannot easily be guaranteed that changes in the variable part of thescreen won't end up in the invariant part, causing a visible videoglitch.

A workable solution according to the present invention is to encode theseparate rectangular parts (2 or more) of the video fully independentfrom each other. Each part would represent a rectangular region of thescreen. Each such region is a multiple of 16 pixels high and a multipleof 16 pixels wide and thus correspond to an integral number of MPEGmacroblocks. All rectangular regions together would precisely cover theentire screen 20 (without overlaps). An NTSC picture, for example, is720 pixels wide and 480 pixels high, corresponding to 45 macroblockswide and 30 macroblocks high. One can, for instance, encode the top 25rows as the invariant part of the picture and make multiple versions ofthe bottom 5 rows to be stitched together with the top 25.

More complicated situations are shown in FIGS. 3 and 4, where the screenis split-up into five and seven rectangular regions respectively, eachan exact multiple of 16 pixels wide and high. In FIG. 3 there is oneregion 22 of the screen variable (with a call to action). In FIG. 4there is an additional logo 24 on the top right hand corner that isvariable.

By running the rectangular regions of the picture through an encoderseparately, the present invention guarantees that motion vector“crosstalk” between the different segments will not occur.

FIG. 5 shows the steps according to an illustrative embodiment. At step1, is the step of determining on the different screen regions, aspreviously described. For this example, there are five differentregions. At step 2, the video for each region is created or extractedfrom source material of other dimensions, as is well known in the art.If the source material is already of the right dimensions, it can beencoded directly. All the segments (including variations) are thenencoded, and then packaged for delivery, step 3. The packaging mayinclude all segments, or be divided up by delivery area or otherparameters. The package is then transferred to the receiving station byany type of transmission, step 4. The receiving station can be a headend, set top box, or other place where the segments will be assembled.The proper segments are selected, and assembled, or stitched, into theappropriate full screen size, step 5. Details for this process areprovided below.

Enabling efficient stitching of separately-encoded pieces of videoaccording to the illustrative embodiment utilizes several steps duringencoding, step 2 FIG. 5. A first requirement on the separately encodedvideos is that they must maintain exactly identical GOP patterns. Forinstance, an IPBBPBBPBBPBB segment can't be stitched together with anIPBPBPBPBPBPB segment. Even though the number of frames is the same inthese GOPs, the differing patterns preclude stitching because aresultant frame can't think of itself as part P (Interframe or forwardprediction frame) and part B (bi-directional predicted frame) at thesame time. Stitching such videos together would effectively meandecoding and subsequently reencoding the video at the point ofreception, thus defeating the purpose.

When encoding the rectangular regions according to the illustrativeembodiment, it is beneficial for VBV buffer size and bitrate for eachregion to be chosen in approximate proportion to the relative sizes ofthe regions. For example, in a two region situation, as shown in FIG. 1,if one region takes 90% of the area, it should use about 90% of theintended final VBV buffer size, while the other region should get 10% orso of each. It is furthermore important to note, as will be explainedbelow, that stitching will typically result in some data expansion, sothe VBV sizes and bitrates actually chosen for encoding should beslightly smaller than the ones that are computed based only on theproportion of the relative region sizes, applied to the fixed desiredVBV buffer size and bitrate. In practice, this means a slight reductionby a fixed factor, usually between 10% and 15%, for each segment. Forexample, for a VBV buffer size of 224 Kbyte and a bitrate of 6000000bits/sec, the sum of the two parts should be about 200 Kbyte for the VBVbuffer and about 5400000 bits/sec. for the bitrate.

Another typical requirement for encoding “stitchable” video segmentsaccording to the illustrative embodiment is that the global streamparameters that control macroblock decoding should be identical acrossclips. In particular, the optional quantization matrices included insequence headers should be the same, as well as any quantization matrixextensions present. Several fields of the picture coding extensionshould also agree across clips, most importantly, the alternate_scanbit, the intra_dc_precision value, and the f_code 4-value array. Mostencoders presently used in the industry usually either pick fixed valuesfor these fields, or they can be instructed to use certain fixed values.The exception to this is the 4-value f_code array which governs thedecoding of motion vectors.

The f-code array contains four elements: one each for forward horizontalmotion, forward vertical motion, backward horizontal motion, andbackward vertical motion. Only B frames actually use all four. P framesonly use the forward components. I frames (Intraframes) don't use themat all.

The values in the f_code array reflect the “worst case” motion vectorsfound in the associated image. A picture with a lot of large-scale grossmotion in it relative to its predecessor picture tends to have largermaximum motion vector sizes than a relatively static picture. Biggermotion vectors are reflected in bigger f_code values, which basicallycontrol the number of bits used to express motion vectors in thepicture. In order to perform video stitching, the f_code values of thevideo frames that must be stitched together must be modified so thatthey are consistent. Subsequently, according to the illustrativeembodiment, the motion vectors that are expressed in terms of thesef_codes reencoded to match the new f_codes. An advantage is that anygiven motion vector can be re-encoded for a larger f_code value, but notnecessarily for a smaller f_code value. Therefore, to be able to stitchtwo or more video frames together, the illustrative embodiment definesthe f_code values for the stitched frame to be at least the maximum ofthe alternatives for any f_code array component. After thus determiningthe new f_code for the stitched frame, the motion vectors of each frameare reencoded in terms of the new f_codes. This reencoding alwaystypically involves some data expansion, but practice has shown it isoften in the order of just 1%.

According to the illustrative embodiment, there are two options tomodifying f_code values and reencoding motion vectors to make videofragments stitchable. The first option is to make this part of theactual stitching process, i.e., in the local stations or set top boxesas shown in FIG. 2. The advantage of this approach is that the packagethat has to be transmitted as small as possible, leading to a saving inbandwidth. However, this means that the stitching work in the localstation is more complex, since all the f_code modification andmotion-vector reencoding has to be done locally.

The second option is to find the maximum f_code values for a given frameacross all variants and modify all the variants (i.e., reencode themotion vectors) for this maximum f_code array before packaging fordistribution. This will simplify the stitching process in the localstation at the expense of needing more bandwidth, and leading toslightly larger (1% or so) stitched videos (since the max. f_code iscomputed across all variants, and not on a per variant basis).

FIG. 5 illustrates the first option, i.e., packaging the video directlyafter encoding, and modifying f_codes and motion vectors afterdistribution. Step 3 illustrates the packaging of the separately encodedsegments into a single package. Step 4 illustrates the distribution ofthat package (using any available transmission mechanism). Step 5 showsthe selection, at the reception point, of a set of segments (one foreach region) to be stitched together. Step 6 in FIG. 6 illustrates themodification of f_code arrays and motion vectors at the point ofreception.

The actual stitching process, after having modified all the f_codearrays and having reencoded all the motion vectors for all the (slicesof the) frames of the videos to be stitched together, is now described.

In MPEG, a single row of macroblocks is encoded as a sequence of one ormore MPEG “slices”, where a slice is a row of macroblocks (onemacroblock high, and one or more macroblocks wide). In a single MPEGvideo frame, these slices are encoded from top to bottom.

The first task to compose a full-screen frame from multiple separatelyencoded smaller frames is to produce the screen-wide rows ofmacroblocks. Simply appending the slices from the different encodedframes for each such row in a left to right order is already sufficient.The only extra work that has to be done for each slice is setting themacroblock_address_increment value in the first macroblock to indicatethe horizontal starting position of the slice in the macroblock row.

Having composed all the individual screen-wide macroblock rows, the nextstep is composing these rows into a full frame. This can be done byappending the rows in a top to bottom order. The only extra work thathas to be done is adjusting the slice slice_vertical_position value ineach slice to indicate how far down the screen from the top the slicegoes in the final stitched frame.

It is important to consider that, although it is perfectly legal MPEG tohave multiple slices per screen-wide row of macroblocks, some decodershave problems with more than 1 slice per macroblock row since this isnot common practice in the industry. It is safer to concatenate two ormore slices into a single full-width slice. Slice-concatenationaccording to the illustrative embodiment is described by the following 6step process.

-   1. All but the first of the slices being concatenated must have    their slice header removed.-   2. The first macroblock of a slice to be appended to a previous    slice may need a macroblock_address_increment adjustment to indicate    how many macroblocks have been skipped between the end of the slice    to its left and the current macroblock. When there is no gap (as is    usually the case), this value will need no change.-   3. If there is a difference between the quantiser_scale_code in use    at the end of a slice and that declared in the excised slice header    on the following slice, the first macroblock of that following slice    will need to contain the correct quantiser_scale_code, indicated by    setting the macroblock_quant_flag in the macroblock, followed by the    appropriate quantiser_scale_code.-   4. The predicted motion vectors at the beginning of a slice    following a previous slice must be updated. At the beginning of a    slice, motion vectors are predicted to be zero, and so the first    motion vectors encoded for a macroblock represent absolute values.    But subsequent macroblocks derive their motion vectors as deltas    from those of the macroblock to their immediate left. Forward and    reverse motion vectors are tracked separately, and in the event that    macroblocks are skipped within the slice, predictions may revert to    zero. The exact rules about how skipped macroblocks affect    predictions differ between P and B frames and field and frame    pictures. In any event, one or more macroblocks at or near the    beginning of a slice to be appended to a previous slice most likely    need to be modified to take into account motion vector predictions    inherited from the previous slice. Once inherited correctly,    macroblocks farther to the right need not be modified.-   5. The “dct_dc_differential” values found in the first macroblock of    an appended slice must be modified to reflect inheritance of    predicted dc levels from the last macroblock of the slice onto which    the appending operation is being performed. Normally slices start    out with known fixed de level assumptions in the first macroblock,    and inherit dc levels, with modification by dct_dc_differential    values, from left to right. Modification of the dct_dc_differential    value is required at the start of an appended slice because it must    base its dc calculation on inheritance from the macroblock to its    left instead of being based on initial fixed values.-   6. The stop code for a slice is a run of 23 zero bits. These stop    bits have to be removed for all but the last appended slice on a    screen row of macroblocks.

FIG. 6 illustrates the stitching of video segments and merging ofslices. Step 7 illustrates the concatenation of slices for single rowsof macroblocks as well as concatenation of such rows into a full-screenpicture. Step 8 illustrates the subsequent merging of multiple slicesfor one screen-wide macroblock row into a single slice.

The final data fields that have to be determined for a complete framethat has thus been stitched together are the vertical_size_value,bit_rate_value, and vbv_buffer_size_value, all in the MPEG sequenceheader, as well as the vbv_delay field in the MPEG picture header.

The value for vertical_size_value is simply the height of the stitchedframe and is hence easy to modify. However, in the case of CBR (ConstantBitRate) MPEG video, to obtain legal values for bit_rate_value,vbv_buffer_size_value, and vbv_delay requires additional work. It isgenerally necessary to add varying amounts of padding between frames ofvideo while appending all frames together, in order to ensure that thevideo has constant bitrate and satisfies the rules for the CBR videobuffer verification (VBV) model that govern the legal playability ofMPEG video. Only after this padding is complete, the values forbit_rate_value, vbv_buffer_size_value, and vbv_delay can be filled infor each frame, step 9. This will be described further in the separatesection below.

In the case of VBR (Variable BitRate) MPEG video, padding is notstrictly necessary. Instead, the system can recalculate the peak(maximum) bitrate of the stream (which might have changed due to thef_code and motion vector adaptation), and fill in this value in thebit_rate_value fields of the video. The vbv_delay fields have aconstant, fixed, value in the case of VBR video, and the value forvbv_buffer_size can simple be chosen as the maximum allowed VBV buffersize for the particular profile and level of the MPEG video (e.g., 224Kbyte for Main Profile/Main Level MPEG video)

As mentioned previously, macroblock data tends to slightly expand toreflect the necessary f_code value changes during stitching, causing anincrease in required bandwidth. Conversely, when streams are stitchedtogether, sequence, GOP, and picture header information from all but oneof them is stripped of to leave just the slices of macroblocks, causinga slight decrease in required bandwidth,

The net effect of f_code-related expansion and header-strippingcontraction usually ends up with a net expansion of raw data to betransmitted. This data expansion will be unevenly distributed, sincesome frames in the stream will be expanded more than others. Therefore,in order to maintain constant bitrate (CBR) and satisfy the associatedVBV buffer models, the new video data must be properly distributed, andthis can be achieved by adding padding bytes between frames of video.

The most straightforward way to pad for VBV legality and constantbitrate is to measure the size of each original frame of video and thestitched frame produced by their concatenation with f_code adjustment asfollows.

-   Let S(n,f) be the size in bytes of frame f of video segment n, where    there are N segments (0, . . . , N−1) that are being stitched    together and F frames of video (0, . . . , F) in each segment.    -   S(f) be the size in bytes of frame f of stitched-together video        (after f_code motion vector adjustment and the discarding of        headers from all but one of the stitched frames)-   Then

E(f)=S(f)/(S(0,f)+S(1,f)+ . . . +S(N−1,f))

is the expansion ratio of frame f of stitched video. Now, let Emax bethe maximum of all values E(0), . . . E(F−1), i.e., the maximumexpansion ratio across all F frames. Practice has shown that a typicalvalue is around 1.1 (a 10% expansion). By padding all stitched frames(except the one(s) that have this maximum expansion rate) with anappropriate number of zero-bytes it is possible to make E(f) the same asthis maximum value Emax for each video frame. Now, furthermore assumingthat the initial frame VBV delay times were equal in the originalseparately encoded clips (which is easy to accomplish with existingencoders) we can define:

VBVmax=(VBV(0)+VBV(1)+ . . . +VBV/(N))*Emax

where

VBV(n) is the VBV buffer size used to encode segment n, and

VBVmax is the VBV buffer size in which the stitched video is guaranteedto run

Padding to a maximum expansion rate as just described is a simple way ofguaranteeing a certain VBV buffer size for the resultant video. KeepingVBVmax below the MPEG defined max. VBV buffer size (e.g., 224 Kbyte forMPEG-2 Main Profile/Main Level, or MP@ML) will guarantee legal videothat any decoder will be able to decode.

One issue with the just described simple padding algorithm is that itcan result in significant (10% or so) expansion of the final stitchedvideo, which can be wasteful. In case the expansion is already donebefore transmission it will also lead to extra bandwidth consumption.

However, a person skilled in the art can see that it is possible toconstruct more intelligent variations of this worst-case paddingalgorithm which reduce the wasted bandwidth and VBV buffer growth byremoving or relocating sections of padding in such a way that buffermodels are not violated.

After the padding of each frame is complete, the values forbit_rate_value, vbv_buffer_size_value, and vbv_delay can finally becomputed and filled in the sequence and picture headers for each frame,thus solving the last required action to complete the stitching process.

Step 9 in FIG. 6 illustrates the final step of padding between frames toachieve the final VBV buffer size for the stitched video sequence in theease of CBR video.

Although the invention has been shown and described with respect toillustrative embodiments thereof, various other changes, omissions andadditions in the form and detail thereof may be made therein withoutdeparting from the spirit and scope of the invention.

It will be understood that various modifications may be made to theembodiments disclosed herein. Therefore, the above description shouldnot be construed as limiting, but merely as exemplification of thevarious embodiments. Those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

1. A method of encoding partial-frame video segments to allow differentpartial-frame video segments to be merged into a full-video frame, saidmethod comprising: dividing said full-video frame area into rectangularregions; obtaining video segments for at least one of said rectangularregions; determining a target buffer size for said video segments for aselected rectangular region; and encoding said video segments for saidselected rectangular region using said determined target buffer size. 2.The method of claim 1 wherein a common GOP pattern is used for encodingall video segments for all of said rectangular regions.
 3. A encodingsystem for encoding partial-frame video segments to allow differentpartial-frame video segments to be merged into a full-video frame, saidencoding system comprising: a rectangular region input to obtaininformation regarding rectangular regions that divide up a full-videoframe, wherein said rectangular regions will have a length and widththat are each 5 a multiple of 16 pixels; a video segment input to obtainvideo segments for at least one of said rectangular regions; a VBVbuffer size determining component, responsive to information regardingrectangular regions obtained by said rectangular region input, said VBVbuffer component to determine a target VBV buffer size for encoding saidvideo segments for a selected rectangular region; wherein said encodingsystem encodes said video segments for said selected rectangular regionusing said determined target VBV buffer size.